This invention relates generally to the field of surgical devices and methods of fixing adjacent vertebrae in the spine. More specifically, the present invention is a device, and a method of using such, which fixes adjacent vertebrae together to prevent movement of the vertebrae with respect to each other. The device may be used during surgical operations or as and implant for permanent spinal fixation.
The history and art surrounding surgical articles and methods to aid in the fusion of adjacent vertebrae is aptly chronicled in U.S. Pat. No. 5,797,909 to Michaelson. Although a recap of that history is not necessary here, an understanding of the Michaelson apparatus and method is necessary to appreciate the present invention.
The Michaelson apparatus and method are believed to represent the current state of the art in temporary fixation of adjacent vertebrae during surgical procedures. As such the Michaelson invention appears to be widely used for spinal fusion operations. Essentially, the primary embodiment of the Michaelson apparatus is a hollow sleeve with teeth at one end. When used in surgeries from the anterior aspect of a patient, the sleeve is driven into adjacent vertebrae over the anterior aspect of the intervertebral space between the vertebrae, which are to be fused. The teeth, when driven into the adjacent vertebrae, work to help stabilize the anterior portions of the two vertebrae and the intervertebral space during the various drilling and surgical operations taking place through the hollow sleeve and within the intervertebral space.
In use, however, the teeth may allow some unwanted relative movement of the vertebrae because they do not stabilize both the anterior and posterior aspects of the vertebrae. This is especially a concern during drilling operations where creating holes with parallel sides in the intervertebral space and the adjacent vertebrae end planes is crucial. For example, when the known apparatus is attached to the anterior aspect of the adjacent vertebrae and drilling is commenced in the intervertebral space from the anterior aspect towards the posterior aspect, the force of the drill may cause a vertebral end plate of the adjacent vertebrae to separate at the posterior aspect of the vertebrae. Because of this movement, the side of the hole drilled in the vertebrae and end plates will taper and will not be parallel when the drill is removed from the hole.
It is believed that this tapering of the walls of the drilled hole can be significant and detrimental. This degree of inaccuracy may lead to misalignment of the fused vertebrae, as well as the exertion of excessive pressure on parts of the implant plug inserted into the hole to fuse the vertebrae. This later consequence is of particular concern where a relatively fragile bone cage plug is used because the irregular pressures can damage the plug. By fixing the adjacent vertebrae in all relative planes the present invention provides for the complete relative stabilization of the adjacent vertebrae, thus ensuring accuracy and precision of surgical procedures performed on the vertebrae. The present invention may also be used as a vertebral implant, permanently stabilized adjacent vertebrae after a surgical procedure, or as a means of correcting a problem with a patient's spine.